The alignment of an anonymous structure defined as a member
of another structure (thanks to -fms-extensions) cannot be
forced with __attribute__((aligned)).
This problem occurs on cygwin with default gcc packages:
gcc version 4.3.2 20080827 (alpha-testing) 1 (GCC)
and:
gcc version 3.4.4 (cygming special, gdc 0.12, using dmd 0.125)
The code below show the exact problem by comparing the sizes and alignments
of a named struct and an anonynous one.
----------------------------------------------------------------------------
#include <stdio.h>
struct nested
{
char a;
char b;
};
struct unaligned
{
char misalign;
struct nested __attribute__((aligned(4)));
};
struct aligned
{
char misalign;
struct nested name __attribute__((aligned(4)));
};
int main(int argc, char * argv[])
{
printf("%d %d - %d %d\n",
sizeof(struct unaligned), sizeof(struct aligned),
__alignof__(struct unaligned), __alignof__(struct aligned));
}
----------------------------------------------------------------------------
options:
gcc-4 -std=c99 -fms-extensions align.c
----------------------------------------------------------------------------
output:
3 8 - 1 4
----------------------------------------------------------------------------
--
Summary: aligned attribute not working on ms-extensions anonymous
struct
Product: gcc
Version: 4.3.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: acalando at free dot fr
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38845
